Method for deoxidizing effervescent steel

ABSTRACT

A METHOD FOR DEOXIDIZING EFFERVESCENT STEEL, IN WHICH A DEOXIDIZING POWDER SUCH AS ALUMINUM IS INJECTED INTO THE CASTING STREAM FROM A LADLE INTO A CASTING MOLD. THE GRAIN SIZE OF THE POWDER IS MAINLY BETWEEN 40 AND 200 MICRONS AND THE POWDER IS UNIFORMLY SUPPLIED TO THE CASTING STREAM DURING AT LEAST 70% OF THE TIME FOR FILLING THE MOLD. IN THE DEVICE THERE IS A COOLING JACKET AROUND THE DISCHARGE END FOR THE POWDER. THE POWDER IS BLOWN BY AIR IN A METERED QUANTITY.

Nov. 7,1972 J. F. DE BLOK ET AL 3,702,151

METHOD FOR DEOXIDIZING EFFERVESCENT STEEL Filed June 18. 1970 INVENTOR J DEBLOAC LEon/AKD shin/5:;

, ATTORNEY United S tes Patent 01 hoe 3,702,151 Patented Nov. 7, 1972 3,702,151 METHOD FOR DEOXIDIZING EFFERVESCENT STEEL Jan F. de Blok, Beverwijk, and Leonard Jansse, Ijmuiden, Netherlands, assignors to Koninklijke Nederlandsche Hoogovens en Staalfabrieken N.V.

Filed June 18, 1970, Ser. No. 47,313 Claims priority, application Netherlands, June 23, 1969, 6909598 Int. Cl. B22d 27/18, 27/20; C21c 7/06 US. Cl. 164-57 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method for deoxidizing effervescent steel in which a deoxidation agent in the condition of a powder is injected into the steel stream during filling of molds from a casting ladle.

Earlier methods have been proposed for blowing a powder into a stream of liquid metal. The use thereof for particular applications was only given in general terms. Wrongly the opinion was that the best results of the blowing of powdery substances into a stream of molten metal for casting were only dependent upon the shape and structure of the device and on the use of inert gases as a carrier fluid for the powdery substances. It was apparently supposed that optimum results could already be obtained if undesired components in the carrier gas, which gas entrains and propels the powder, could be excluded from the reaction, and if sufiicient care was given to the shape and direction of the stream of the reacting powder blown into the stream of metal.

It is remarked that for deoxidizing effervescent steel such a method of blowing powder has only found quite limited application. Other methods consist in that periodically quantities of larger grains of a deoxidiing agent are strewed into the casting ladle or that a tape or wire of a deoxidizing agent is shot into the casting mold. It has appeared that the manner of metering and the grain size of the deoxidizing agent, usually aluminum, is particularly important for the quality of the final product. The present invention is based upon the new idea that parts or lanes with a different behaviour in the final treatment of sheet material cold rolled from steel slabs or the like made from effervescently solidified steel ingots are caused by the manner of metering and by the grain size of the deoxidizing agent.

1 Moreover it has appeared therewith that when applying the known devices for blowing powdery deoxidizing agents there is a quite considerable variation in possibilities for influencing the quality of the final rolled product.

In fact it appears therewith that other factors influence this.final quality much more than factors such as the shape of the nozzle openings for the powdery material or the question whether the carrying gas is inert or not.

In the light of the above the present invention consists in that in a method as given in the preamble the grain size of the powder is essentially limited to between 40 microns and 200 microns, in which for at least 50% of the powder the grains have a largest linear dimension between 75 microns and 150 microns and in which the powder is uniformly metered when being supplied to the stream of casting metal during at least of the time for filling the casting mold. In particular favourable results are obtainable in applying the invention it for about 65% of the powder the grains have a linear dimension between microns and 150 microns and if the metering of the powder to the casting stream takes place during at least of the casting time.

When choosing these circumstances, in particular in combination with measures to be discussed later, it appears that in the further processing of the rolled product which is finally obtained from the steel thus cast, no irregularities or deviations in quality in the product, which could be traced back to an influence of deoxidation of the steel, occur any more. Apparently both the larger and the finer grains of the deoxidizing agents may cause irregularities in distribution of this agent over the steel, which irregularities are maintained during the entire further processing of the steel. It should be deemed surprising that a so much restricted field of grain dimensions for the powder could be found in which the distribution of the deoxidizing agent over the steel is optimum. Of the greatest importance is moreover the fact that the metering of the powder takes place as uniformly as possible in time. This is obtained by metering and supplying the powder in the period in which the casting stream is as stationary as possible. Preferably no powder is blown into the stream during the beginning and the end of the casting.

The best results with the new method are obtained, when blowing aluminum powder into the casting stream, if the charging of the gas with powder is adjusted so that per liter of gas it contains about 1.9 to 2.2 grams of aluminum and that 700 to 1200 grams of powder per minute are blown into the metal. It has even appeared therewLh that the blowing of the powder with air is in no respect inferior to the blowing with an inert gas. An explanation for the favourable results of the method for such a choice of the supply of the powder with air could be the following:

If less powder is entrained by the air, a too high quantity of air is necessary to bring the totally required quantity of powder into the casting stream. This large quantity of air cannot be blown in the shape of a concentrated beam onto the casting stream and moreover has a too strong cooling effect upon this casting stream. If on the contrary too much powder is loaded in the air, a too low quantity of air is blown out to give to the powder sufficient impetus. As a result thereof the contact of the powder with the casting stream could be insufiicient and irregular.

Although in essence the quantity per unit time of the carrying air and of the powder are determining the result of the blowing of this powder into the stream, it appears that, to a lesser extent, also the speed of the air in the powder and air stream could influence the result of the deoxidation. This speed relates to the greater or smaller divergence of the powder stream. Preferably according to the invention the air speed in the stream of powder and air is adjusted to 40 to 60 meters per second and in particular preferably at about 50 meters per second.

Depending upon the local circumstances at which the powder has to be metered, the mixture of powder and gas will be preheated more or less by the surroundings shortly before the blowing thereof into the metal. It has appeared that the danger is not always imaginative that for instance aluminum powder will be heated to such a high temperature that it becomes sticky. In that case the metering of the powder and thus also the uniformity of the quality of the final steel product will be influenced in an unfavourable manner.

It has appeared that this disadvantage could be removed according to the invention by cooling the mixture of powder and gas shortly before the blowing into the casting stream.

Other advantages of the invention will be apparent from the following description of an embodiment of the invention, in connection with the accompanying drawings, in which:

FIG. 1 shows a device diagrammatically in longitudinal section.

FIG. 2 shows more or less diagrammatically this device in perspective view with part of a ladle, ingot mold and casting stream.

In FIG. 1 reference numeral 1 indicates a supply tube for a mixture of aluminum powder and air. This supply tube is connected to a chamber 2, in which a supply funnel 3 and a duct 4 for air under pressure open. Duct 4 is narrower at its discharge end to give a passage of A2". The mutual positioning of the duct 4 and the funnel 3 in the chamber 2 is such that its causes the desired quantity of aluminum powder from the funnel 3 to be sucked in and entrained by the air under pressure leaving duct 4.

In this duct 4 a control valve 6 is arranged. By adjusting this control valve 6 and by adjusting the position of the duct 4, which means by having it extend into the chamher 2 over the desired distance it is possible to adjust the quantity of aluminum powder to be loaded into the air within wide limits. Thereto the duct 4 could be slidable longitudinally throughv its hole in the Wall of chamber 2 in a suitable sliding seal in this hole.

Dependent upon the volume of metal to 'be taken up by the casting mold and dependent upon the composition of the steelto be cast therein it is possible to determine the required quantity of aluminum powder before casting. This quantity is then brought into funnel 3 before casting.

It is remarked that, although this example speaks about aluminum powder, the invention is not restricted thereto. The same is of course true where in this specification air under pressure is indicated, which could also be another gas.

It will be clear that for other applications other deoxidizing agents or suitable mixtures or alloys of suitable elements could be added or that other gases could be used for conveying the powder.

Close to its discharge end the supply tube 1 is surrounded by a cooling jacket 7. This is connected through a hose or flexible branch duct 8 to the supply duct for air under pressure upstream of the control valve 6. At its free end the supply tube 1 is provided with a flange 9, so that cooling jacket 7 at this end has a radially directed outflow opening. The cooling air flowing out is thereby discharged in a direction which is transverse to the direction of the powder stream. Ducts 4 and 8 are connected to a source of air at a pressure of to 6 atmospheres. It has appeared that suflicient cooling is obtained if per minute about 2 Nm. of air is passed through the cooling jacket 7.

In FIG. 2 it has been shown diagrammatically in what way the device of FIG. 1 is used.

A casting ladle 11 filled with liquid steel is suspended over a casting mold 10 such as a known ingot mold and said ladle 11 has an outflow opening for the metal in its bottom, which can be closed by a stopper rod valve or the like. About at the level of the upper rim of the casting mold 10 there isa platform 12 for the operating personnel to allow them to check the casting process visually. The casting streams from the ladle 11 is indicated by 13. An operator manipulates the device according to FIG. 1, which is suspended pivotally to a suitable structure 14, which forms part of the casting ladle 11. Thus it is possible to bring the supply tube 1 at the desired location opposite the casting stream 13. The device is connected to a source of air under. pressure by a hose 15 connected to duct 4. After opening the outflow opening in the bottom of the ladle and after the casting jet 13 has obtained a more or less stationary shape and condition the operator opens the control valve 6, so that blowing of the aluminum powder into the casting stream begins. As a rule the metering of the quantity of powder in funnel 3 and the adjustment of control valve 6 will be predetermined so that the supply of aluminum powder continues during the period in which the casting stream flows on without varying its shape more than negligibly. However, the operator also has the possibility to vary the supply of aluminum or to stop it entirely by operating the control valve 6 if the need thereto is felt during casting.

By way of example it may be mentioned that an ingot mold was filled by 20 tons by weight of steel intended for the manufacture of cold rolled sheet material suited for pressing for instance hub covers or bumpers of motor cars. To this charge 900 grams of aluminum had to be added. This aluminium was chosen as aluminum powder with grain sizes in essence between 40 microns and 200 microns. In a sieve test it was found that this powder was composed of fractions of the following dimensions:

Percent Not over 37 microns 0.7 From:

37 to 50 microns 2.1

50 to 75 microns 7.8

75 to microns 25.2

105 to microns 34.0

Total 67.0

150 to 200 microns 24.0

200 to 300 microns 4.3

300 to 420 microns 1.7

The casting time of the block to be cast was adjusted to be 1 minute and 15 seconds, the metering of the powder was adjusted to be 900 grams per minute. The powder was blown with a quantity of air under pressure of 450 liters per minute. The load factor of the mixture thus was 2 grams of aluminum per liter of The outflow speed of the aluminum powder from the discharge tube 1 was measured to be 46.7 in. per second. The discharge tube was cooled by 2.3 Nm. of air under pressure per minute.

0f the total casting period of 1 minute and 15 seconds the aluminum powder was blown into the casting stream during one minute. It appeared that with this rather critical choice of the conditions of the process a cold rolled material was obtained from the steel ingot which even for the most critical bending and deep drawing operations did not show surface irregularities or failures which could be considered to be caused by the aluminum as a deoxidizing agent.

We claim:

1. An improved method for the deoxidizing of effervescent steel, said method being one which comprises (a) injecting an oxidizing agent into the casting stream during the filling of a casting mold from a ladle, wherein the improvement comprises (b) effecting delivery of the deoxidizing agent to the casting stream in the form of a powder having its grain size essentially limited to between 40 and 200 microns and at least 50% of which has a largest linear dimension between 75 and 150 microns, and

(c) uniformly metering said delivery over at least 70% of the time of filling of the mold by said stream.

2. An improved method as claimed in claim 1, wherein the deoxidizing agent is aluminum powder and wherein (d) the aluminum powder is delivered to the casting stream in a jet of air,

(e) said delivery is eifected at a rate of from 700 to 1200 grams of aluminum powder per minute, and

(f) the ratio of aluminum powder to air in the jet is in the range of about 1.9 to 2.2 grams of aluminum per liter of air.

3. An improved method as claimed in claim 1, wherein (d) the deoxidizing powder is delivered to the casting stream in a jet of air, and

(e) the speed of said jet of air lies in the range of 40 to 60 meters per second.

4. An improved method as claimed in claim 1, wherein (d) the deoxidizing powder is delivered to the casting stream in a jet of air, and

(e) the mixture of powder and air in said jet is cooled shortly before it is blown into the casting stream.

References Cited UNITED STATES PATENTS L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R. 

